Multiaxial nonwoven fabric, and method of making the same

ABSTRACT

A multiaxial nonwoven fabric is disclosed which is comprised of a selected warp material and a multiplicity of selected continuous yarns assembled in a specified lay pattern and bonded on to the warp material. Each of the yarns is oriented in a scalene or right-angled triangle shape, and the resulting yarn assembly is built of intersections at least in warp, weft and oblique axes, whereby structural strength and dimensional stability are greatly improved. A method and an apparatus are also disclosed for producing the fabric.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention is concerned with nonwoven fabrics and more particularlywith a multiaxial nonwoven fabric in which a multiplicity of selectedcontinuous yarns are assembled in a specified lay pattern by mechanicalinterlocking. The invention further relates to a method of and anapparatus for producing such multiaxial fabric.

By the term multiaxial nonwoven fabric used herein is meant a fabricdesigned to have its constituent yarns intersected in two or moredifferent axes and even in a weftwise axis.

2. Prior Art

Certain nonwoven fabrics have been developed and marketed, one of whichis formed of a number of parallel continuous yarns obliquely crossed andadhesively bonded to a substrate such as paper, film, aluminum foil orcloth. Another fabric is of a triaxial structure having bound anadditional group of arranged warps. Both fabrics are formed typically bya method in which the basic or constituent yarns are allowed toreciprocally run at right angle to the path of travel of a conveyor beltand when brought into hooking engagement, upon arrival at their turningpoints, with two arrays of pins each located on and along onelongitudinal edge of the belt, they are crossed obliquely with oneanother.

In such prior fabrics, however, the basic yarns each are oriented in theshape of an isosceles triangle when one vertex is taken against the basebetween the two other vertices. These fabrics, though physicallyadequate in both a warp and an oblique direction, are mechanically weakand dimensionally unstable in a weft direction.

To cope with the above problems, the conveyor belt is required to travelat low speed so as to reciprocate the basic yarns while being heldobliquely at an identical angle and nearly at a weftwise level,rendering the final fabric laterally dense. Such mode of formation isundesirable for practical purposes as it is rather tedious andcomplicated, less productive and yet susceptible to qualityirregularities and cost burdens.

SUMMARY OF THE INVENTION

With the foregoing difficulties of the prior art in view, the presentinvention seeks to provide an improved nonwoven fabric of a multiaxialtype which has a multiplicity of continuous yarns laid to intersect inwarp and countersymmetrically oblique axes and even in a weft or nearlyweft axis, thus exhibiting not only a good balance of structuralstrength and dimensional stability characteristics but also aestheticalappearance. The invention also provides a method of and an apparatus forthe production of such nonwoven fabric in a one-step operation and athigh speed and with high efficiency and great economy.

The fabric of the invention finds application particularly as a basematerial for FRP plastics and as a material of reinforcement in varioussectors of industry.

According to a first aspect of the invention, there is provided amultiaxial nonwoven fabric comprising (a) a warp material, and (b) amultiplicity of continuous yarns laid in tensioned, intersected relationby successive bending at a predetermined angle and on two opposite sidesof the fabric corresponding to two widthwise ends of the warp material,thereby forming a yarn assembly in which each of the yarns is orientedto define a scalene or right-angled triangle as determined by taking onevertex against the straight line between the two other vertices, andsubsequently by adhesive bonding onto the warp material.

According to a second aspect of the invention, there is provided amethod of producing a multiaxial nonwoven fabric which comprises (a)driving a conveyor belt to travel, the belt being provided on and alongrespective longitudinal edges thereof with two arrays of pins of apredetermined pitch, (b) reciprocating a multiplicity of parallelcontinuous yarns at a predetermined angle between the arrays of pins,the yarns being fed at the same pitch as the pins, (c) advancing thepins in the same number as the yarns with one reciprocation of the yarnsin such a manner that the yarns are brought into hooking engagement,upon arrival at their turning points, with the pins in either array andbent in zigzag form with varying lengths of the yarns at the going andcoming routes, thereby forming a yarn assembly having the yarnsintersected in weft and oblique axes, and (d) overlying and bonding awarp material onto the yarn assembly prior to or after release from thearrays of pins.

According to a third aspect of the invention, there is provided anapparatus for producing a multiaxial nonwoven fabric which comprises (a)a conveyor belt provided on and along respective longitudinal edgesthereof with two arrays of pins of a predetermined pitch, (b) twotraverser supports positioned at forward and rearward sides of thetravel path of the belt and disposed over and across the belt, each ofthe supports including a pair of parallel rods and a traverser mountedfor sliding movement on and along the rods, the supports beingoppositely inclined at a predetermined angle with respect to the travelpath of the belt, (c) two rows of yarn guides disposed in the traversersat the same pitch and direction as the arrays of pins, (d) meanscontrolling the speed of the belt at which to advance the pins in thesame number as the yarn guides, (e) means feeding a warp material on tothe belt, and (f) means bonding the warp material to the resulting yarnassembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation, partly enlarged, of one laypattern of the prior art.

FIGS. 2A and 3A are views similar to FIG. 1, but showing preferred laypatterns embodying the present invention.

FIGS. 2B, 3B and 3C are views of modified forms of the patterns shown inFIGS. 2A and 3A.

FIGS. 4 and 5 are views, seen in plan and from elevation, of theapparatus constructed in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, there is shown a certain multiaxial nonwovenfabric of the prior art in which a multiplicity of continuous yarns arelaid in zigzag form, the yarns being bent at identical angles on twoopposite sides of the fabric. A single continuous yarn, indicated in abold line and designated at y, is run to assume an isosceles trianglewhen a vertex a is taken against the base defined by two other verticesb and c. With this lay pattern, inadequate weftwise strength isnecessarily developed as noted hereinbefore.

A multiaxial nonwoven fabric according to the invention is comprised ofa selected warp material and a multiplicity of selected continuous yarnsassembled in a unique fashion and attached onto the warp material.

In certain preferred lay patterns contemplated under the invention, theyarns are laid in tensioned, intersected relation by bending atidentical angles and on two opposite sides of the fabric, the fabricsides being taken to correspond to two widthwise ends of the warpmaterial (not shown), as seen from FIGS. 2A and 3A. Importantly, aconstituent yarn Y can be oriented, despite bending at one and the sameangle on both sides, in the shape of a scalene triangle ABC (FIG. 2A) ora right-angled triangle ABC (FIG. 3A). The two types of angles aredetermined by taking one vertex A against the base between two othervertices B and C. Such yarn orientation is sharply contrasted to theprior lay pattern. The resulting yarn assembly is thereafter bonded ontothe warp material, whereby the desired nonwoven fabric is provided.

Modified forms of the lay patterns of FIGS. 2A and 3A are illustrated inFIGS. 2B and 3B in which a different group of yarns Y' is overlaid inthe form of an inverted scalene triangle A'B'C' (FIG. 2B) or an invertedright-angled triangle A'B'C' (FIG. 3B) on the first mentioned patterns(FIGS. 2A and 3A). Particularly preferred is a nonwoven fabric shown inFIG. 3B, which fabric is formed with a group of arranged warps X furtheroverlaid by bonding to the ABC-A'B'C' structure. Such fabric has threedifferent groups of yarns Y, Y' and X intersected in warp, weft andcountersymmetrically oblique axes, leading to sufficient strength in thetetraaxial direction.

FIG. 3C shows still another preferred form of the fabric of FIG. 3B.This form results from slight modification of the vertices A and A' onthe two right-angled triangles ABC and A'B'C' with the results that allthe constituent yarns may intersect substantially in a straight line andhence improve aesthetical appearance.

Specific examples of yarns include organic, inorganic and metallicfibers, stranded rovings, tape yarns, split yarns and the like. Warpmaterials used herein may be selected for instance from papers, films,aluminum foils, foamed sheets, different nonwoven fabrics, arrangedwarps and the like. Preferred among these warp materials are arrangedwarps to be overlaid on either or both of the upper and lower surfacesof the yarn assembly and then bonded to the intersected portions.

The invention is also contemplated for the provision of a method of andan apparatus for producing the above specified fabric.

An apparatus, provided in accordance with the invention and shown at 10in FIGS. 4 and 5, is constructed essentially with a conveyor belt 11 andtwo sets of traverser supports 20 and 30. The belt 11 is provided on andalong two longitudinal edges with an array 12 of pins 13 and a companionarray 14 of pins 15 both for yarn hooking, the pins 13 and 15 beingspaced apart at a given pitch. The support 20 is made up of a pair ofparallel rods 21 and 22 and an elongate traverser 23 secured at bothends to the rods 21 and 22 for sliding movement in known manner. Thesupport 30, composed of two rods 31 and 32 and a traverser 33, isdevised substantially identical to the support 20 as better seen fromFIG. 4.

The supports 20 and 30 are positioned at rearward and forward sides withrespect to the travel path of the belt 11 as indicated by the arrow inFIG. 4 and disposed to straddle the belt 11. Both supports shouldimportantly be inclined oppositely at a predetermined angle α to thebelt path.

Mounted on the traversers 23 and 33 are rows of yarn guides 24 and 34,respectively, for guiding two groups of selected continuous yarns 25 and35 onto the belt 11 from yarn feeding means (not shown). The guides 24and 34 are placed in aligned relation with the pin arrays 12 and 14 andmay be formed for example of pipes of reduced diameter and increasednumber.

Designated at 16 and 17 are first and second yarn assemblies resultingfrom the reciprocal action of the traversers 23 and 33 as describedlater. A pair of rolls 20 are located adjacent to a front end of thebelt path for subsequent bonding of the yarn assemblies with a warpmaterial 18 (FIG. 4) and if necessary with a similar material 19 (FIG.5).

In operation, the belt 11 is driven to travel on suitable driving means,whereas the traversers 23 and 33 are actuated to feed the yarns 25 ontothe belt 11 from the guide 24 to thereby form the first yarn assembly 16and the second yarn assembly 17 by further feeding the yarns 35 from theguide 34 on to the first assembly 16. The yarns 25 and 35 are run tobring into hooking engagement, on arrival at their turning points, withthe pin arrays 12 and 14 and thus bent obliquely with one another.

To achieve the desired lay of the first group of yarns 25, the followingconditions will now be assumed with equations (1) and (2). ##EQU1##where L : distance between pin arrays 12 and 14

S : distance at which belt 11 advances with one reciprocation oftraverser 23

β : angle at which yarns 25 reciprocate warpwise

θ : angle at which yarns 25 run obliquely

By strict observance of equations (1) and (2), the yarns are hooked atvarying length and in zigzag form with the pins 13 and 15 at the goingand coming routes of the traverser 23. The first yarn assembly 16 isthus provided in a scalene triangle shape as shown in FIG. 2A.

If the rods 21 and 22 of the traverser support 20 are placed in parallelto one side of a scalene triangle defined by L as the height and S asthe base, equation (1) is rearranged as

    cot α=S/2L

    tan β=∞

this meaning that the yarns 25 get displaced at a right angle, i.e. on aweftwise level, to the warp axis when the traverser 23 moves obliquelytoward the travel path of the belt 11.

In the case of S=L and hence cot α=1/2 and α=63°25', equation (2) isarranged to give

    tan θ=1

the yarns 25 being therefore run at an angle of 45° to the warp axiswhen the traverser 23 is moved to a counteroblique direction.

The second yarn assembly 17 may suitably be formed by overlying theassembly 16 with the second group of yarns 35 fed out of the yarn guide34 of the traverser 33. The front traverser 33 is reciprocally moved atthe same stroke speed as and with the same yarn number as the reartraverser 23. The yarns 35 are laid to assume an inverted scalenetriangle, and the resulting assembly 17 is built with yarn intersectionsin the countersymmetrically oblique axes.

The yarn assembly 16 or 17 is thereafter bound on its lower surface withthe warp material 18 being introduced onto the belt 11, followed bypassage through the rolls 20 to ensure firm bonding and by subsequentrelease from the pin arrays 12 and 14, after which the desired nonwovenfabric is obtained. The assembly may if necessary be superposed even onan upper surface, while in bonding on the lower surface, with the warpmaterial 19 supplied from other than the belt 11 and after being takenout in sandwiched form, then transported for fixation on another set ofrolls (not shown). The fixation may be effected using hot-melt oremulsion type binders or their combinations. The warps 18 and 19 mayconveniently be precoated with a suitable binder such as, for example,either one of the binders specified above.

According to additional preferred embodiments of the method of theinvention, a multiplicity of continuous yarns are laid into a yarnassembly having intersections in oblique and weft axes by reciprocationbetween the arrays of pins and in parallel to an orbit determined by oneside of an isosceles triangle, which triangle is defined by taking asthe height the distance between the arrays of pins and as the base thedistance at which the belt travels with one reciprocation of the yarns,and subsequently by displacement of the axial centers of the yarns at aright angle to the warp axis at either of the going and coming routes.Further, a multiplicity of continuous yarns in a plurality of sets maybe laid into a yarn assembly having intersections in more than two axesby feeding to the belt at different respective positions andsubsequently by reciprocation between the arrays of pins and in parallelto an orbit defined to cross the belt at an angle different from orsymmetrical to the warp axis.

EXAMPLE OF THE INVENTION

The following example is given to further illustrate the presentinvention, but should not be construed as limiting the invention.

In the arrangement shown in FIGS. 4 and 5, a conveyor belt was usedwhich was provided on its longitudinal edges with two arrays of pins of1.5 mm in diameter, 15 mm in length, 7 mm in pitch and 560 mm inarray-to-array width. Two traverser supports, each provided thereon witha slidable traverser, were positioned at forward and rearward sides ofthe travel path of the belt and disposed over and across the belt. Thesupports were oppositely inclined at 63°25' with respect to the beltpath. A row of 40 pipes of small sizes, 2 mm in inside diameter and 30mm in length and of 14 mm in pitch was mounted as a yarn guide on eachof the traversers. The pipes each were arranged to piercingly project 15mm beneath the traverser.

The driving gear ratio and pulley diameter were determined such that thebelt was advanced at a distance of 560 mm upon turning of the pulley bya 1/2 revolution while the front and rear traversers were being movedwith one reciprocation at a stroke of 640 mm and at a revolution of 20on the supports. Each of the traversers was so mounted as to protrude,when in return motion, about 10 mm out of the pin array on either aright or a left side.

The belt was driven to travel at a speed of 18 m/min with two groups ofglass rovings of 10,000 deniers, 40 ends in one group, fed on to thebelt through the yarn guides. One group of rovings from the reartraverser was hooked with alternate pins in the arrays (at 14 mm pitch)and with two adjacent pins on the protruded side so that the rovingswere laid in zigzag form in a weft and an oblique direction at 45°.Another group of rovings guided from the front traverser was broughtinto hooking engagement with intermediate pins located between the abovealternated pins and thus laid in an inverted zigzag shape.

There was obtained a yarn assembly in which 80 rovings were intersectedat a pitch of 7 mm in the weft axis and at 45° in thecountersymmetrically oblique axes.

Subsequently, rovings of 10,000 deniers were interconnected as warpswith the yarn assembly formed above, which rovings were precoated with ahot-melt binder. To be more specific, a first group of 41 ends arrangedat a pitch of 14 mm was guided onto the belt, whereas a second group of40 ends arranged in like manner was shifted at a pitch of 7 mm and fedonto heating rolls located adjacent to a front end of the belt path. Asthe belt was continued to travel, the yarn assembly was bound on a lowersurface with the first roving group and then released successively fromthe pin arrays, followed by transport to the rolls for adhesion on anupper surface with the second roving group. The yarn assembly was takenout of the rolls which was sandwiched between the two groups of warpsand bound at the intersected portions.

The method and apparatus of the invention have been found to produce anonwoven fabric of a multiaxial structure having its constituent yarnsintersected regularly in the warp, weft and countersymmetrically obliqueaxes, i.e. in the tetraaxial direction, as seen from FIG. 3C. The fabricis highly mechanically strong, dimensionally stable and ornamentallyvisible.

While the invention has been described in conjunction with certainspecific embodiments thereof, it should be noted that various changesand modifications may be made as conceived by those skilled in the artwithin the scope of the appended claims.

What is claimed is:
 1. A method of producing a multiaxial nonwovenfabric which comprises:(a) driving a conveyor belt along a path oftravel, said belt being provided with two arrays of pins of apredetermined pitch extending on and along respective oppositelongitudinal edges thereof; (b) reciprocating a multiplicity of parallelcontinuous yarns at a predetermined angle between said arrays of pinsand at the same pitch as said pins; (c) advancing said pins in the samenumber as said yarns with one reciprocation of the yarns in such amanner that said yarns are brought into hooking engagement, upon arrivalat their turning points, with said pins in either array and bent inzigzag form with varying lengths of the yarns at their going and comingroutes, thereby forming a yarn assembly having said yarns intersected onweft and oblique axes by reciprocation between said arrays of pins andparallel to an orbit determined by one side of an isosceles triangle,said isosceles triangle being defined by taking as the height thereofthe distance between said arrays of pins and as the base thereof thedistance at which said belt travels with one reciprocation of saidyarns, and by subsequent displacement of the axial centers of said yarnsat a right angle to the warp axis at either one of the going and comingroutes; and (d) overlaying and bonding a warp material on a lower or anupper surface or both surfaces of said yarn assembly prior to or afterrelease thereof from said arrays of pins.
 2. The method of claim 1wherein said yarn assembly is sandwiched between an upper and a lowergroup of warp yarns, followed by release from said arrays of pins and bytransport to rolls located adjacent to a front end of the travel path ofsaid belt, and subsequently bonded at the intersected portions duringpassage through said rolls.
 3. The method of claim 1 wherein amultiplicity of continuous yarns in a plurality of sets are laid into ayarn assembly having intersections in more than two axes by feeding tosaid belt at different respective positions and subsequently byreciprocation between said arrays of pins and in parallel to an orbitdefined to cross said belt at an angle different from or symmetrical tothe warp axis.
 4. The method of claim 1 wherein said yarns comprise anorganic yarn, inorganic yarn, metallic yarn, stranded roving, tape yarnor split yarn.
 5. The method of claim 1 wherein said warp materialcomprises a paper, film, aluminum foil, foamed sheet, nonwoven fabric orarranged warp.
 6. The method of claim 1 wherein said warp material isprecoated with a binder selected from a hot-melt or emulsion-type binderor a combination thereof.
 7. The method of claim 1 wherein said warpmaterial is bonded to said yarn assembly by a binder.
 8. The method ofclaim 1 wherein said binder comprises a hot-melt or emulsion-type binderor a combination thereof.
 9. A method of producing a multiaxial nonwovenfabric, comprising the steps of: providing first and second arrays ofpins disposed along respective first and second longitudinal axes;reciprocating in first and second directions a plurality of continuousyarns between the first and the second arrays of pins; longitudinallyadvancing the first and the second arrays of pins at different speedsrelative to the reciprocating plurality of continuous yarns so as tobring the plurality of continuous yarns into hooking engagement with thefirst and the second arrays of pins; and controlling the differentrelative speeds to dispose different respective lengths of yarn betweenthe first and second arrays of pins depending on the reciprocatingdirection so as to form a yarn assembly having a zigzag form byintersecting the continuous yarns on weft and oblique axes byreciprocation between the pin arrays and parallel to an orbit determinedby one side of an isosceles triangle and by subsequent displacement ofthe centers of the continuous yarns at a right angle to the warp axis.10. A method of producing a multiaxial nonwoven fabric according toclaim 9; wherein the continuous yarns are reciprocated at apredetermined angle relative to the first and second longitudinal axes.11. A method of producing a multiaxial nonwoven fabric according toclaim 9; wherein the first and second arrays of pins are disposed alongrespective longitudinal axes of a conveyor belt.
 12. A method ofproducing a multiaxial nonwoven fabric according to claim 9; wherein thefirst and second arrays of pins are disposed at a given pitch, and thereciprocating plurality of continuous yarns are separated from eachother by the same given pitch.
 13. A method of producing a multiaxialnonwoven fabric according to claim 9; wherein the plurality ofcontinuous yarns are brought into hooking engagement with the first andsecond arrays of pins at respective turning points of reciprocation. 14.A method of producing a multiaxial nonwoven fabric according to claim 9;further comprising the step of bonding the yarn assembly to a warpmaterial.
 15. A method of producing a multiaxial nonwoven fabricaccording to claim 9; further comprising providing at least one otherplurality of continuous yarns; reciprocating the at least one otherplurality of continuous yarns in other first and second directions; andlongitudinally advancing the first and second arrays of pins atdifferent speeds relative to the at least one other plurality ofcontinuous yarns dependent on the other first and second directions.